This invention relates to cathode ray display tubes, and is particularly concerned with the base of such tubes that provides for passing and isolating a number of electrically conductive pins that convey operating voltages into the tube envelope.
Cathode ray tubes used in television picture tubes, and in CRT monitors displaying a variety of information, typically have a narrow neck terminated by a plurality of electrically conductive pins extending axially from the neck. The pins may comprise a number of closely spaced, low-voltage pins, and at least one high-voltage pin widely spaced from the low-voltage pins. The potentials conducted by the low-voltage pins may range from less than one volt to one kilovolt, for example. The potentials conducted by the high-voltage pin are typically in the range of six to twelve kilovolts, or greater. In certain television tube applications, an additional very high potential termed the "anode potential" is in the range of 25-32 kilovolts, and is introduced through the tube envelope by means of an "anode button" which passes through the anode in the cathode ray tube funnel region.
Electrical connection to the pins is typically made by a socket which provides for connecting by means of a plurality of frictional members which slidably contact each pin. The members are attached to a plurality of lead wires which in turn make connection to various components of the ancillary electrical chassis, such as the power supply and scanning circuits. To ensure electrical isolation of the high-voltage pins from the low-voltage pins, the aforedescribed base may have a plurality of axially and radially outwardly extending insulating walls which isolate the pins one from the others to prevent inter-pin arcing. The pins which conduct the high voltages may be further isolated from the low-voltage pins and from each other, by an elaborate system of insulating walls and cavities. A base of this type, which in conjunction with a socket system, provides for high voltage arc prevention between adjacent pins is described and claimed in U.S. Pat. No. 4,075,531, assigned to the assignee of the present invention.
It is a common practice to supplement the insulation provided by the base by the addition of an electrically insulative material into a cavity surrounding the pins. The insulative material is also an adhesive which provides for adhering base the to the neck terminus. The insulative material may comprise a thermo-setting polymer adhesive.
A separable, socket-type connection may be inexpedient in certain applications such as, for example, a cathode ray tube used in a vehicular dashboard display, or an aircraft cockpit display. As the electrical contact made by the socket with the base is frictional, near-zero-resistance electrical connections are not assured. While of little consequence where higher voltages are concerned, near-zero-resistance connections are essential in very low voltage connections, such as the filament connections in directly heated cathodes. A cathode of this type may require, for example, a voltage of 0.64, with a tolerance of .+-.0.02 volt. Any appreciable variance from the limits specified affects the warm-up time. In case of an under-voltage condition, the cathode may be subject to premature failure due to poisoning from under heating. Further, with a frictional contact arrangement, the pins are exposed to the environment and are thus subject to corrosion, dust and moisture which can appreciably increase the electrical resistance of the contact areas with time.